THE ROLE OF CYANIDE IN THE INTERACTION OF ETHYL XANTHATE WITH GALENA

Ultraviolet-visible (UV/Vis) and Fourier transform-infrared (FT-IR) spectroscopy were used to examine the kinetics of ethyl xanthate adsorption onto galena at pH 9. In general the rate and extent of ethyl xanthate adsorption increased with the pulp electrochemical potential (Eh). FT-IR studies using the attenuated total reflectance (ATR) mode confirmed the presence of lead ethyl xanthate species on galena, with no evidence of diethyl dixanthogen. The effect of cyanide on the adsorption kinetics of ethyl xanthate on galena depends on the Eh as well as the order of reagent addition. Simultaneous addition of ethyl xanthate and cyanide results in an increase in the rate and extent of ethyl xanthate adsorption at Eh values < + 200 mV, whereas at higher Eh values cyanide had little effect on ethyl xanthate adsorption. Furthermore, cyanide addition to galena with preadsorbed ethyl xanthate led to increased xanthate adsorption, behaviour which was more pronounced at lower Eh values. A possible mechanism for this activation process is proposed, where cyanide interacts with the sulphur moiety of galena, leaving a lead-rich galena surface which is more susceptible to ethyl xanthate interaction. In contrast to pyrite and pyrrhotite surfaces, no competitive adsorption between cyanide and ethyl xanthate for the galena surface was evident. This finding was in agreement with X-ray photoelectron spectroscopy (XPS) and FT-IR studies which did not detect any surface cyano species on galena.